The unfolded protein response in secretory cell function

The evolution of developmental biology through conceptual and technological revolutions

Developmental biology-the study of the processes by which cells, tissues, and organisms develop and change over time-has entered a new golden age. After the molecular genetics revolution in the 80s and 90s and the diversification of the field in the early 21st century, we have entered a phase when powerful technologies provide new approaches and open unexplored avenues. Progress in the field has been accelerated by advances in genomics, imaging, engineering, and computational biology and by emerging model systems ranging from tardigrades to organoids. We summarize how revolutionary technologies have led to remarkable progress in understanding animal development. We describe how classic questions in gene regulation, pattern formation, morphogenesis, organogenesis, and stem cell biology are being revisited. We discuss the connections of development with evolution, self-organization, metabolism, time, and ecology. We speculate how developmental biology might evolve in an era of synthetic biology, artificial intelligence, and human engineering.

Curcumin and Resveratrol: Nutraceuticals with so Much Potential for Pseudoachondroplasia and Other ER-Stress Conditions

Natural products with health benefits, nutraceuticals, have shown considerable promise in many studies; however, this potential has yet to translate into widespread clinical use for any condition. Notably, many drugs currently on the market, including the first analgesic aspirin, are derived from plant extracts, emphasizing the historical significance of natural products in drug development. Curcumin and resveratrol, well-studied nutraceuticals, have excellent safety profiles with relatively mild side effects. Their long history of safe use and the natural origins of numerous drugs contrast with the unfavorable reputation associated with nutraceuticals. This review aims to explore the nutraceutical potential for treating pseudoachondroplasia, a rare dwarfing condition, by relating the mechanisms of action of curcumin and resveratrol to molecular pathology. Specifically, we will examine the curcumin and resveratrol mechanisms of action related to endoplasmic reticulum stress, inflammation, oxidative stress, cartilage health, and pain. Additionally, the barriers to the effective use of nutraceuticals will be discussed. These challenges include poor bioavailability, variations in content and purity that lead to inconsistent results in clinical trials, as well as prevailing perceptions among both the public and medical professionals. Addressing these hurdles is crucial to realizing the full therapeutic potential of nutraceuticals in the context of pseudoachondroplasia and other health conditions that might benefit.

Tanshinone IIA attenuates valvular interstitial cells' calcification induced by oxidized low density lipoprotein via reducing endoplasmic reticulum stress

Recent studies revealed that endoplasmic reticulum (ER) stress played an emerging role of in valve calcification. Tanshinone IIA (TanIIA) has been a research hotspot in cardiovascular diseases. Previously we found that sodium TanIIA dampened the pathological phenotype transition of valvular interstitial cells (VICs) by affecting ER stress published in Chinese Journal. Here, we test the hypothesis that TanIIA attenuates the pro-osteogenic effects of oxidized low-density lipoprotein (oxLDL) in VICs by reducing induction of ER stress. Patients' aortic valve (AV) was collected, and porcine VICs were cultured for in vitro model. ER stress markers were tested in human leaflets by immunostaining. Immunoblotting were used to test the osteoblastic factors such as Runx2, osteocalcin, and ER stress markers GRP78, CHOP, XBP1, etc. Alkakine phosphate (ALP) activity assay were used to test the activity of ALP kinase. Pro-inflammatory gene expression was detected by polymerase chain reaction. As a result, ER stress markers were elevated in patients' calcified AVs. OxLDL induced osteogenesis and inflammation via promoting ER stress. TanIIA attenuated oxLDL induced ER stress. TanIIA also inhibited theosteoblastic factors and inflammatory cytokine expressions in VICs. In conclusion, our data provide evidence that TanIIA exerts anti-inflammation and anti-osteogenic effects in VICs by attenuating ER stress, and ER stress acts as an important regulator in oxLDL induced VICs' phenotype transition.

Metformin sensitizes AML cells to venetoclax through endoplasmic reticulum stress-CHOP pathway

Venetoclax inhibits acute myeloid leukaemia by inhibiting BCL-2 targeting, and a combination regimen with venetoclax has been explored. Although these regimens produce better clinical results, the vast majority of patients still suffer from disease recurrence or primary drug resistance. Metformin has been demonstrated to induce apoptosis in cancer cells. However, whether it can synergize with venetoclax and the underlying mechanisms of metformin-induced apoptosis are not fully understood. In this study, we investigated the effect of metformin and venetoclax on the growth of AML cells in vitro and in vivo. In both Molm13 and THP-1 cell lines, metformin and venetoclax synergistically inhibited the proliferation and induced apoptosis of leukaemia cells. Most importantly, the combination of metformin and venetoclax treatment significantly increased the expression levels of the endoplasmic reticulum (ER) stress-related marker CHOP, for example, in AML cell lines. Knockdown of CHOP markedly attenuated the metformin- and venetoclax-induced cell apoptosis. Moreover, the combination of metformin and venetoclax demonstrated prominent anti-leukaemia effects in xenograft models and bone marrow samples from AML patients. In summary, the combination of metformin and venetoclax showed enhanced anti-leukaemia activity with acceptable safety in AML patients, representing a new combinatorial strategy worth further clinical investigation to treat AML.

Spinocerebellar ataxia 38: structure-function analysis shows ELOVL5 G230V is proteotoxic, conformationally altered and a mutational hotspot

Fatty acid elongase ELOVL5 is part of a protein family of multipass transmembrane proteins that reside in the endoplasmic reticulum where they regulate long-chain fatty acid elongation. A missense variant (c.689G>T p.Gly230Val) in ELOVL5 causes Spinocerebellar Ataxia subtype 38 (SCA38), a neurodegenerative disorder characterized by autosomal dominant inheritance, cerebellar Purkinje cell demise and adult-onset ataxia. Having previously showed aberrant accumulation of p.G230V in the Golgi complex, here we further investigated the pathogenic mechanisms triggered by p.G230V, integrating functional studies with bioinformatic analyses of protein sequence and structure. Biochemical analysis showed that p.G230V enzymatic activity was normal. In contrast, SCA38-derived fibroblasts showed reduced expression of ELOVL5, Golgi complex enlargement and increased proteasomal degradation with respect to controls. By heterologous overexpression, p.G230V was significantly more active than wild-type ELOVL5 in triggering the unfolded protein response and in decreasing viability in mouse cortical neurons. By homology modelling, we generated native and p.G230V protein structures whose superposition revealed a shift in Loop 6 in p.G230V that altered a highly conserved intramolecular disulphide bond. The conformation of this bond, connecting Loop 2 and Loop 6, appears to be elongase-specific. Alteration of this intramolecular interaction was also observed when comparing wild-type ELOVL4 and the p.W246G variant which causes SCA34. We demonstrate by sequence and structure analyses that ELOVL5 p.G230V and ELOVL4 p.W246G are position-equivalent missense variants. We conclude that SCA38 is a conformational disease and propose combined loss of function by mislocalization and gain of toxic function by ER/Golgi stress as early events in SCA38 pathogenesis.

Unfolded protein response factor ATF6 augments T helper cell responses and promotes mixed granulocytic airway inflammation

The unfolded protein response (UPR) is associated with the risk of asthma, including treatment-refractory severe asthma. Recent studies demonstrated a pathogenic role of activating transcription factor 6a (ATF6a or ATF6), an essential UPR sensor, in airway structural cells. However, its role in T helper (TH) cells has not been well examined. In this study, we found that ATF6 was selectively induced by signal transducer and activator of transcription6 (STAT6) and STAT3 in TH2 and TH17 cells, respectively. ATF6 upregulated UPR genes and promoted the differentiation and cytokine secretion of TH2 and TH17 cells. T cell-specific Atf6-deficiency impaired TH2 and TH17 responses in vitro and in vivo and attenuated mixed granulocytic experimental asthma. ATF6 inhibitor Ceapin A7 suppressed the expression of ATF6 downstream genes and TH cell cytokines by both murine and human memory clusters of differentiation 4 (CD4)+ T cells. At the chronic stage of asthma, administration of Ceapin A7 lessened TH2 and TH17 responses, leading to alleviation of both airway neutrophilia and eosinophilia. Thus, our results demonstrate a critical role of ATF6 in TH2 and TH17 cell-driven mixed granulocytic airway disease, suggesting a novel option to combat steroid-resistant mixed and even T2-low endotypes of asthma by targeting ATF6.

Endoplasmic reticulum stress: a novel targeted approach to repair bone defects by regulating osteogenesis and angiogenesis

Bone regeneration therapy is clinically important, and targeted regulation of endoplasmic reticulum (ER) stress is important in regenerative medicine. The processing of proteins in the ER controls cell fate. The accumulation of misfolded and unfolded proteins occurs in pathological states, triggering ER stress. ER stress restores homeostasis through three main mechanisms, including protein kinase-R-like ER kinase (PERK), inositol-requiring enzyme 1ɑ (IRE1ɑ) and activating transcription factor 6 (ATF6), collectively known as the unfolded protein response (UPR). However, the UPR has both adaptive and apoptotic effects. Modulation of ER stress has therapeutic potential for numerous diseases. Repair of bone defects involves both angiogenesis and bone regeneration. Here, we review the effects of ER stress on osteogenesis and angiogenesis, with emphasis on ER stress under high glucose (HG) and inflammatory conditions, and the use of ER stress inducers or inhibitors to regulate osteogenesis and angiogenesis. In addition, we highlight the ability for exosomes to regulate ER stress. Recent advances in the regulation of ER stress mediated osteogenesis and angiogenesis suggest novel therapeutic options for bone defects.

Unconventional Activation of IRE1 Enhances TH17 Responses and Promotes Neutrophilic Airway Inflammation

Treatment-refractory severe asthma manifests a neutrophilic phenotype associated with TH17 responses. Heightened unfolded protein responses (UPRs) are associated with the risk of asthma, including severe asthma. However, how UPRs participate in the deregulation of TH17 cells leading to this type of asthma remains elusive. In this study, we investigated the role of the UPR sensor IRE1 in TH17 cell function and neutrophilic airway inflammation. We found that IRE1 is induced in fungal asthma and is highly expressed in TH17 cells relative to naïve CD4+ T cells. Cytokine (e.g. IL-23) signals induce the IRE1-XBP1s axis in a JAK2-dependent manner. This noncanonical activation of the IRE1-XBP1s pathway promotes UPRs and cytokine secretion by TH17 cells. Ern1 (encoding IRE1)-deficiency decreases the expression of ER stress factors and impairs the differentiation and cytokine secretion of TH17 cells. Genetic ablation of Ern1 leads to alleviated TH17 responses and airway neutrophilia in a Candida albicans asthma model. Consistently, IL-23 activates the JAK2-IRE1-XBP1s pathway in vivo and enhances TH17 responses and neutrophilic infiltration into the airway. Taken together, our data indicate that IRE1, noncanonically activated by cytokine signals, promotes neutrophilic airway inflammation through the UPRmediated secretory function of TH17 cells. The findings provide a novel insight into the fundamental understanding of IRE1 in TH17-biased TH2-low asthma.

Matrix in Medicine: Health Consequences of Mutant Cartilage Oligomeric Matrix Protein and its relationship to abnormal growth and to joint degeneration

Cartilage oligomeric matrix protein (COMP), an extracellular matrix protein, has been shown to enhance proliferation and mechanical integrity in the matrix, supporting functions of the growth plate and articular cartilage. Mutations in COMP cause pseudoachondroplasia (PSACH), a severe dwarfing condition associated with premature joint degeneration and significant lifelong joint pain. The MT (mutant)-COMP mouse mimics PSACH with decreased limb growth, early joint degeneration and pain. Ablation of endoplasmic reticulum stress CHOP signaling eliminated pain and prevented joint degeneration. The health effects of mutant COMP are discussed in relation to cellular/chondrocyte stress in the growth plate, articular cartilage and nearby tissues, and the implications for therapeutic approaches. There are many similarities between osteoarthritis and mutant-COMP protein-induced joint degeneration, suggesting that the relevance of findings in the joints may extend beyond PSACH to idiopathic primary OA.

The Xbp1-regulated transcription factor Mist1 restricts antibody secretion by restraining Blimp1 expression in plasma cells

Antibody secretion by plasma cells provides acute and long-term protection against pathogens. The high secretion potential of plasma cells depends on the unfolded protein response, which is controlled by the transcription factor Xbp1. Here, we analyzed the Xbp1-dependent gene expression program of plasma cells and identified Bhlha15 (Mist1) as the most strongly activated Xbp1 target gene. As Mist1 plays an important role in other secretory cell types, we analyzed in detail the phenotype of Mist1-deficient plasma cells in Cd23-Cre Bhlha15 ^fl/fl mice under steady-state condition or upon NP-KLH immunization. Under both conditions, Mist1-deficient plasma cells were 1.4-fold reduced in number and exhibited increased IgM production and antibody secretion compared to control plasma cells. At the molecular level, Mist1 regulated a largely different set of target genes compared with Xbp1. Notably, expression of the Blimp1 protein, which is known to activate immunoglobulin gene expression and to contribute to antibody secretion, was 1.3-fold upregulated in Mist1-deficient plasma cells, which led to a moderate downregulation of most Blimp1-repressed target genes in the absence of Mist1. Importantly, a 2-fold reduction of Blimp1 (Prdm1) expression was sufficient to restore the cell number and antibody expression of plasma cells in Prdm1 ^Gfp/+ Cd23-Cre Bhlha15 ^fl/fl mice to the same level seen in control mice. Together, these data indicate that Mist1 restricts antibody secretion by restraining Blimp1 expression, which likely contributes to the viability of plasma cells.

miR-4734 conditionally suppresses ER stress-associated proinflammatory responses

Prolonged metabolic stress can lead to severe pathologies. In metabolically challenged primary fibroblasts, we assigned a novel role for the poorly characterized miR-4734 in restricting ATF4 and IRE1-mediated upregulation of a set of proinflammatory cytokines and endoplasmic reticulum stress-associated genes. Conversely, inhibition of this miRNA augmented the expression of those genes. Mechanistically, miR-4734 was found to restrict the expression of the transcriptional activator NF-kappa-B inhibitor zeta (NFKBIZ), which is required for optimal expression of the proinflammatory genes and whose mRNA is targeted directly by miR-4734. Concordantly, overexpression of NFKBIZ compromised the effects of miR-4734, underscoring the importance of this direct targeting. As the effects of miR-4734 were evident under stress but not under basal conditions, it may possess therapeutic utility towards alleviating stress-induced pathologies.

Hemocytes and fat body cells, the only professional immune cell types in Drosophila, show strikingly different responses to systemic infections

The fruit fly Drosophila is an excellent model to study the response of different immunocompetent organs during systemic infection. In the present study, we intended to test the hypothesis that the only professional immune organs of the fly, the fat body and hemocytes, show substantial similarities in their responses to systemic infection. However, comprehensive transcriptome analysis of isolated organs revealed highly divergent transcript signatures, with the few commonly regulated genes encoding mainly classical immune effectors from the antimicrobial peptide family. The fat body and the hemocytes each have specific reactions that are not present in the other organ. Fat body-specific responses comprised those enabling an improved peptide synthesis and export. This reaction is accompanied by transcriptomic shifts enabling the use of the energy resources of the fat body more efficiently. Hemocytes, on the other hand, showed enhanced signatures related to phagocytosis. Comparing immune-induced signatures of both cell types with those of whole-body responses showed only a minimal correspondence, mostly restricted again to antimicrobial peptide genes. In summary, the two major immunocompetent cell types of Drosophila show highly specific responses to infection, which are closely linked to the primary function of the respective organ in the landscape of the systemic immune response.

XBP1 impacts lung adenocarcinoma progression by promoting plasma cell adaptation to the tumor microenvironment

Background: The activation of X-box binding protein 1 (XBP1) plays an essential role in the unfolded protein response (UPR) of the endoplasmic reticulum (ER). XBP1 is commonly expressed in various tumors and is closely related to tumorigenesis and progression. However, the role of XBP1 in lung adenocarcinoma (LUAD), especially the prognostic value of its alternative splicing isoforms, remains largely unknown.

Methods: The LUAD datasets were retrieved from the The Cancer Genome Atlas, ArrayExpress and Gene Expression Omnibus. GEPIA2 and meta-analysis were employed to explore the prognostic value, and bioinformatics analysis with the TIMER2.0 database was used to investigate immune cell infiltration. We performed single-cell analyses to identify cell types with high XBP1 expression. In addition, polymerase chain reaction (PCR) and DNA sequencing were performed to verify the authenticity of the new spliceosome.

Results: In this study, we found that high expression of XBP1 was significantly associated with a good prognosis, and XBP1 expression was significantly positively correlated with B cell infiltration in LUAD. In addition, we found that high-level expression of a novel splicing isoform, XBP1 (XBP1-003), improved the prognosis of LUAD. Protein structural analysis demonstrated that XBP1-003 has several specific protein domains that are different from those of other XBP1 isoforms, indicating a unique function of this isoform in LUAD.

Conclusion: All these results suggest that XBP1 plays an antitumorigenic role in LUAD through alternative splicing, which may be related to the adaptation of plasma cells. This sheds new light on the potential strategy for LUAD prognosis evaluation and immunotherapy.

Identification of Gene Modules and Hub Genes Associated with Sporisorium scitamineum Infection Using Weighted Gene Co-Expression Network Analysis

Sporisorium scitamineum is a biotrophic fungus responsible for sugarcane smut disease. To investigate the key genes involved in S. scitamineum infection, we conducted RNA sequencing of sugarcane sprouts inoculated with S. scitamineum teliospores. A weighted gene co-expression network analysis (WGCNA) showed that two co-expressed gene modules, MEdarkturquoise and MEpurple—containing 66 and 208 genes, respectively—were associated with S. scitamineum infection. The genes in these two modules were further studied using Gene Ontology (GO) enrichment analysis, pathogen-host interaction (PHI) database BLASTp, and small secreted cysteine-rich proteins (SCRPs) prediction. The top ten hub genes in each module were identified using the Cytohubba plugin. The GO enrichment analysis found that endoplasmic reticulum-related and catabolism-related genes were expressed during S. scitamineum infection. A total of 83 genes had homologs in the PHI database, 62 of which correlated with pathogen virulence. A total of 21 proteins had the characteristics of small secreted cysteine-rich proteins (SCRPs), a common source of fungal effectors. The top ten hub genes in each module were identified, and seven were annotated as Mig1-Mig1 protein, glycosyl hydrolase, beta-N-acetylglucosaminidase, secreted chorismate mutase, collagen, mRNA export factor, and pleckstrin homology domain protein, while the remaining three were unknown. Two SCRPs—SPSC_06609 and SPSC_04676—and three proteins—SPSC_01958, SPSC_02155, and SPSC_00940—identified in the PHI database were also among the top ten hub genes in the MEdarkturquoise and MEpurple modules, suggesting that they may play important roles in S. scitamineum infection. A S. scitamineum infection model was postulated based on current findings. These findings help to deepen the current understanding of early events in S. scitamineum infection.

Age-related endoplasmic reticulum stress represses testosterone synthesis via attenuation of the circadian clock in Leydig cells

Senile animals exhibit a high risk of elevated endoplasmic reticulum (ER) stress, attenuated circadian clock, and impaired steroidogenesis in testes. However, how these three processes are intertwined in mouse Leydig cells remains unclear. In this study, a mouse model of aging and hydrogen peroxide (H₂O₂)-induced senescent TM3 Leydig cells were used to dissect the connections among ER stress, circadian oscillators, and steroidogenesis in Leydig cells. Additionally, thapsigargin (Tg, 60 nM)/tunicamycin (Tm, 60 ng/mL)-induced ER stress were established to investigate the underlying mechanisms by which ER stress regulated testosterone synthesis via circadian clock-related signaling pathways in TM3 cells and primary Leydig cells. Elevated ER stress, attenuated circadian clock, and diminished steroidogenesis were detected in the testes of aged mice (24-month-old) and H₂O₂-induced (200 μM) senescent TM3 cells in comparison with their control groups. Tg/Tm-induced ER stress reduced the transcription of the circadian clock and steroidogenic genes in TM3 cells and LH-treated (100 ng/mL) primary Leydig cells. Furthermore, 4-phenylbutyric acid (4-PBA, 1 μM), an inhibitor of ER stress, alleviated the inhibitory effect of Tg-mediated ER stress on Per2:Luc oscillations in primary Leydig cells isolated from mPer2^Luc knock-in mice, and attenuated the repressive effect of H₂O₂-induced or Tg-mediated ER stress on the transcription of circadian clock and steroidogenic genes expression and testosterone synthesis in TM3 cells. Collectively, these data indicate that age-related ER stress represses testosterone synthesis via attenuation of the circadian clock in Leydig cells.

FK506-Binding Protein 11 Is a Novel Plasma Cell-Specific Antibody Folding Catalyst with Increased Expression in Idiopathic Pulmonary Fibrosis

Antibodies are central effectors of the adaptive immune response, widespread used therapeutics, but also potentially disease-causing biomolecules. Antibody folding catalysts in the plasma cell are incompletely defined. Idiopathic pulmonary fibrosis (IPF) is a fatal chronic lung disease with increasingly recognized autoimmune features. We found elevated expression of FK506-binding protein 11 (FKBP11) in IPF lungs where FKBP11 specifically localized to antibody-producing plasma cells. Suggesting a general role in plasma cells, plasma cell-specific FKBP11 expression was equally observed in lymphatic tissues, and in vitro B cell to plasma cell differentiation was accompanied by induction of FKBP11 expression. Recombinant human FKBP11 was able to refold IgG antibody in vitro and inhibited by FK506, strongly supporting a function as antibody peptidyl-prolyl cis-trans isomerase. Induction of ER stress in cell lines demonstrated induction of FKBP11 in the context of the unfolded protein response in an X-box-binding protein 1 (XBP1)-dependent manner. While deficiency of FKBP11 increased susceptibility to ER stress-mediated cell death in an alveolar epithelial cell line, FKBP11 knockdown in an antibody-producing hybridoma cell line neither induced cell death nor decreased expression or secretion of IgG antibody. Similarly, antibody secretion by the same hybridoma cell line was not affected by knockdown of the established antibody peptidyl-prolyl isomerase cyclophilin B. The results are consistent with FKBP11 as a novel XBP1-regulated antibody peptidyl-prolyl cis-trans isomerase and indicate significant redundancy in the ER-resident folding machinery of antibody-producing hybridoma cells.

Fungal Extracellular Vesicles Are Involved in Intraspecies Intracellular Communication

Fungal infections are associated with high mortality rates in humans. The risk of fungal diseases creates the urgent need to broaden the knowledge base regarding their pathophysiology. In this sense, the role of extracellular vesicles (EVs) has been described to convey biological information and participate in the fungus-host interaction process. We hypothesized that fungal EVs work as an additional element in the communication routes regulating fungal responses in intraspecies interaction systems. In this respect, the aim of this study was to address the gene regulation profiles prompted by fungal EVs in intraspecies recipient cells. Our data demonstrated the intraspecies uptake of EVs in pathogenic fungi, such as Candida albicans, Aspergillus fumigatus, and Paracoccidioides brasiliensis, and the effects triggered by EVs in fungal cells. In C. albicans, we evaluated the involvement of EVs in the yeast-to-hypha transition, while in P. brasiliensis and A. fumigatus the function of EVs as stress transducers was investigated. P. brasiliensis and A. fumigatus were exposed to an inhibitor of glycosylation or UV light, respectively. The results demonstrated the role of EVs in regulating the expression of target genes and triggering phenotypic changes. The EVs treatment induced cellular proliferation and boosted the yeast to hyphal transition in C. albicans, while they enhanced stress responsiveness in A. fumigatus and P. brasiliensis, establishing a role for EVs in fungal intraspecies communication. Thus, EVs regulate fungal behavior, acting as potent message effectors, and understanding their effects and mechanism(s) of action could be exploited in antifungal therapies. IMPORTANCE Here, we report a study about extracellular vesicles (EVs) as communication mediators in fungi. Our results demonstrated the role of EVs from Candida albicans, Aspergillus fumigatus, and Paracoccidioides brasiliensis regulating the expression of target genes and phenotypic features. We asked whether fungal EVs play a role as message effectors. We show that fungal EVs are involved in fungal interaction systems as potent message effectors, and understanding their effects and mechanisms of action could be exploited in antifungal therapies.

Holistic insights from pollen omics: co-opting stress-responsive genes and ER-mediated proteostasis for male fertility

Sexual reproduction in flowering plants takes place without an aqueous environment. Sperm are carried by pollen through air to reach the female gametophyte, though the molecular basis underlying the protective strategy of the male gametophyte is poorly understood. Here we compared the published transcriptomes of Arabidopsis thaliana pollen, and of heat-responsive genes, and uncovered insights into how mature pollen (MP) tolerates desiccation, while developing and germinating pollen are vulnerable to heat stress. Germinating pollen expresses molecular chaperones or "heat shock proteins" in the absence of heat stress. Furthermore, pollen tubes that grew through pistils at basal temperature showed induction of the endoplasmic reticulum (ER) stress response, which is a characteristic of stressed vegetative tissues. Recent studies show MP contains mRNA-protein (mRNP) aggregates that resemble "stress" granules triggered by heat or other stresses to protect cells. Based on these observations, we postulate that mRNP particles are formed in maturing pollen in response to developmentally programmed dehydration. Dry pollen can withstand harsh conditions as it is dispersed in air. We propose that, when pollen lands on a compatible pistil and hydrates, mRNAs stored in particles are released, aided by molecular chaperones, to become translationally active. Pollen responds to osmotic, mechanical, oxidative, and peptide cues that promote ER-mediated proteostasis and membrane trafficking for tube growth and sperm discharge. Unlike vegetative tissues, pollen depends on stress-protection strategies for its normal development and function. Thus, heat stress during reproduction likely triggers changes that interfere with the normal pollen responses, thereby compromising male fertility. This holistic perspective provides a framework to understand the basis of heat-tolerant strains in the reproduction of crops.

Endoplasmic reticulum stress promotes local immunoglobulin E production in allergic rhinitis

BACKGROUND

The role of endoplasmic reticulum (ER) stress in the pathogenesis of allergic rhinitis (AR) remains elusive.

METHODS

Real-time polymerase chain reaction (RT-PCR), immunohistochemistry, and western blotting analyses were performed to detect the expression of ER stress and unfolded protein response markers: 78-kDa glucose-regulated protein (GRP78), C/EBP homologous protein (CHOP), activating transcription factor 6 (ATF6α), spliced X-box binding protein 1 (sXBP-1), and phosphorylated eukaryotic initiation factor 2α (p-eIF2α), in inferior turbinate tissue samples from patients with AR and non-AR controls. Nasal tissues from patients with AR were cultured ex vivo and treated with 4-phenylbutyric acid (4-PBA), an ER stress inhibitor.

RESULTS

Compared to those in non-AR controls, the mRNA and protein levels of GRP78, CHOP, ATF6α, sXBP-1, and p-eIF2α were significantly increased in nasal tissues from patients with AR. GRP78 and CHOP were mainly expressed in CD138+ plasma cells in nasal tissues from patients with AR. The frequency of IgE+CD138+ plasma cells was significantly higher in nasal tissues from patients with AR than that in non-AR controls. IgE levels in nasal secretions and tissues were positively correlated with GRP78 and CHOP mRNA levels in the nasal tissues. After 4-PBA treatment, the protein expression of GRP78, CHOP, ATF6α, sXBP-1, and p-eIF2α was significantly reduced in cultured AR-derived nasal tissues, and IgE levels were simultaneously decreased in cultured supernatants.

CONCLUSIONS

ER stress may be involved in the regulation of local IgE production in patients with AR. Inhibition of ER stress potentially provides a therapeutic avenue in AR by reducing local IgE production.

LEVEL OF EVIDENCE

NA.

Progress of Signaling Pathways, Stress Pathways and Epigenetics in the Pathogenesis of Skeletal Fluorosis

Fluorine is widely dispersed in nature and has multiple physiological functions. Although it is usually regarded as an essential trace element for humans, this view is not held universally. Moreover, chronic fluorosis, mainly characterized by skeletal fluorosis, can be induced by long-term excessive fluoride consumption. High concentrations of fluoride in the environment and drinking water are major causes, and patients with skeletal fluorosis mainly present with symptoms of osteosclerosis, osteochondrosis, osteoporosis, and degenerative changes in joint cartilage. Etiologies for skeletal fluorosis have been established, but the specific pathogenesis is inconclusive. Currently, active osteogenesis and accelerated bone turnover are considered critical processes in the progression of skeletal fluorosis. In recent years, researchers have conducted extensive studies in fields of signaling pathways (Wnt/β-catenin, Notch, PI3K/Akt/mTOR, Hedgehog, parathyroid hormone, and insulin signaling pathways), stress pathways (oxidative stress and endoplasmic reticulum stress pathways), epigenetics (DNA methylation and non-coding RNAs), and their inter-regulation involved in the pathogenesis of skeletal fluorosis. In this review, we summarised and analyzed relevant findings to provide a basis for comprehensive understandings of the pathogenesis of skeletal fluorosis and hopefully propose more effective prevention and therapeutic strategies.

Candida albicans Sfp1 Is Involved in the Cell Wall and Endoplasmic Reticulum Stress Responses Induced by Human Antimicrobial Peptide LL-37

Candida albicans is a commensal fungus of humans but can cause infections, particularly in immunocompromised individuals, ranging from superficial to life-threatening systemic infections. The cell wall is the outermost layer of C. albicans that interacts with the host environment. Moreover, antimicrobial peptides (AMPs) are important components in innate immunity and play crucial roles in host defense. Our previous studies showed that the human AMP LL-37 binds to the cell wall of C. albicans, alters the cell wall integrity (CWI) and affects cell adhesion of this pathogen. In this study, we aimed to further investigate the molecular mechanisms underlying the C. albicans response to LL-37. We found that LL-37 causes cell wall stress, activates unfolded protein response (UPR) signaling related to the endoplasmic reticulum (ER), induces ER-derived reactive oxygen species and affects protein secretion. Interestingly, the deletion of the SFP1 gene encoding a transcription factor reduced C. albicans susceptibility to LL-37, which is cell wall-associated. Moreover, in the presence of LL-37, deletion of SFP1 attenuated the UPR pathway, upregulated oxidative stress responsive (OSR) genes and affected bovine serum albumin (BSA) degradation by secreted proteases. Therefore, these findings suggested that Sfp1 positively regulates cell wall integrity and ER homeostasis upon treatment with LL-37 and shed light on pathogen-host interactions.

Activation of salt Inducible Kinases, IRE1 and PERK leads to Sec bodies formation in Drosophila S2 cells

The phase separation of the non-membrane bound Sec bodies occurs in Drosophila S2 cells by coalescence of components of the endoplasmic reticulum (ER) exit sites under the stress of amino acid starvation. Here, we address which signaling pathways cause Sec body formation and find that two pathways are critical. The first is the activation of the salt-inducible kinases (SIKs; SIK2 and SIK3) by Na⁺ stress, which, when it is strong, is sufficient. The second is activation of IRE1 and PERK (also known as PEK in flies) downstream of ER stress induced by the absence of amino acids, which needs to be combined with moderate salt stress to induce Sec body formation. SIK, and IRE1 and PERK activation appear to potentiate each other through the stimulation of the unfolded protein response, a key parameter in Sec body formation. This work shows the role of SIKs in phase transition and re-enforces the role of IRE1 and PERK as a metabolic sensor for the level of circulating amino acids and salt.

This article has an associated First Person interview with the first author of the paper.

Summary: In S2 cells, the phase-separated Sec bodies form upon the combined activation of salt-inducible kinases, IRE1 and PERK.

State-of-the-Art Dermatophyte Infections: Epidemiology Aspects, Pathophysiology, and Resistance Mechanisms

The burden of fungal infections is not widely appreciated. Although these infections are responsible for over one million deaths annually, it is estimated that one billion people are affected by severe fungal diseases. Mycoses of nails and skin, primarily caused by fungi known as dermatophytes, are the most common fungal infections. Trichophyton rubrum appears to be the most common causative agent of dermatophytosis, followed by Trichophyton interdigitale. An estimated 25% of the world’s population suffers from dermatomycosis. Although these infections are not lethal, they compromise the quality of life of infected patients. The outcome of antidermatophytic treatments is impaired by various conditions, such as resistance and tolerance of certain dermatophyte strains. The adage “know your enemy” must be the focus of fungal research. There is an urgent need to increase awareness about the significance of these infections with precise epidemiological data and to improve knowledge regarding fungal biology and pathogenesis, with an emphasis on adaptive mechanisms to tackle adverse conditions from host counteractions. This review outlines the current knowledge about dermatophyte infections, with a focus on signaling pathways required for fungal infection establishment and a broad perspective on cellular and molecular factors involved in antifungal resistance and tolerance.

Calcium-Collagen Coupling is Vital for Biomineralization Schedule

Biomineralization is a chemical reaction that occurs in organisms in which collagen initiates and guides the growth and crystallization of matched apatite minerals. However, there is little known about the demand pattern for calcium salts and collagen needed by biomineralization. In this study, natural bone biomineralization is analyzed, and a novel interplay between calcium concentration and collagen production is observed. Any quantitative change in one of the entities causes a corresponding change in the other. Translocation-associated membrane protein 2 (TRAM2) is identified as an intermediate factor whose silencing disrupts this relationship and causes poor mineralization. TRAM2 directly interacts with the sarcoplasmic/endoplasmic reticulum calcium ATPase 2b (SERCA2b) and modulates SERCA2b activity to couple calcium enrichment with collagen biosynthesis. Collectively, these findings indicate that osteoblasts can independently and directly regulate the process of biomineralization via this coupling. This knowledge has significant implications for the developmentally inspired design of biomaterials for bone regenerative applications.

Coordinated signaling of activating transcription factor 6α and inositol-requiring enzyme 1α regulates hepatic stellate cell-mediated fibrogenesis in mice

Liver injury and the unfolded protein response (UPR) are tightly linked, but their relationship differs with cell type and injurious stimuli. UPR initiation promotes hepatic stellate cell (HSC) activation and fibrogenesis, but the underlying mechanisms are unclear. Despite the complexity and overlap downstream of UPR transducers inositol-requiring protein 1α (IRE1α), activating transcription factor 6α (ATF6α), and protein kinase RNA-like ER kinase (PERK), previous research in HSCs primarily focused on IRE1α. Here, we investigated the fibrogenic role of ATF6α or PERK in vitro and HSC-specific UPR signaling in vivo. Overexpression of ATF6α, but not the PERK effector activating transcription factor 4 (ATF4), promoted HSC activation and fibrogenic gene transcription in immortalized HSCs. Furthermore, ATF6α inhibition through Ceapin-A7, or Atf6a deletion, disrupted transforming growth factor β (TGFβ)-mediated activation of primary human hepatic stellate cells (hHSCs) or murine hepatic stellate cells (mHSCs), respectively. We investigated the fibrogenic role of ATF6α in vivo through conditional HSC-specific Atf6a deletion. Atf6a^HSCΔ/Δ mice displayed reduced fibrosis and HSC activation following bile duct ligation (BDL) or carbon tetrachloride (CCl₄)-induced injury. The Atf6a^HSCΔ/Δ phenotype differed from HSC-specific Ire1a deletion, as Ire1a^HSCΔ/Δ mice showed reduced fibrogenic gene transcription but no changes in fibrosis compared with Ire1a^fl/fl mice following BDL. Interestingly, ATF6α signaling increased in Ire1a^Δ/Δ HSCs, whereas IRE1α signaling was upregulated in Atf6a^Δ/Δ HSCs. Finally, we asked whether co-deletion of Atf6a and Ire1a additively limits fibrosis. Unexpectedly, fibrosis worsened in Atf6a^HSCΔ/ΔIre1a^HSCΔ/Δ mice following BDL, and Atf6a^Δ/ΔIre1a^Δ/Δ mHSCs showed increased fibrogenic gene transcription. ATF6α and IRE1α individually promote fibrogenic transcription in HSCs, and ATF6α drives fibrogenesis in vivo. Unexpectedly, disruption of both pathways sensitizes the liver to fibrogenesis, suggesting that fine-tuned UPR signaling is critical for regulating HSC activation and fibrogenesis.NEW & NOTEWORTHY ATF6α is a critical driver of hepatic stellate cell (HSC) activation in vitro. HSC-specific deletion of Atf6a limits fibrogenesis in vivo despite increased IRE1α signaling. Conditional deletion of Ire1α from HSCs limits fibrogenic gene transcription without impacting overall fibrosis. This could be due in part to observed upregulation of the ATF6α pathway. Dual loss of Atf6a and Ire1a from HSCs worsens fibrosis in vivo through enhanced HSC activation.

The Stress of Lung Aging: Endoplasmic Reticulum and Senescence Tête-à-Tête

Beyond the structural changes, features including the dysregulation of endoplasmic reticulum (ER) stress response and increased senescence characterize the lung aging. ER stress response and senescence have been reported to be induced by factors like cigarette smoke. Therefore, deciphering the mechanisms underlying ER and senescent pathways interaction has become a challenge. In this review we highlight the known and unknown regarding ER stress response and senescence and their cross talk in aged lung.

ER Stress and Unfolded Protein Response in Leukemia: Friend, Foe, or Both?

The unfolded protein response (UPR) is an evolutionarily conserved adaptive signaling pathway triggered by a stress of the endoplasmic reticulum (ER) lumen compartment, which is initiated by the accumulation of unfolded proteins. This response, mediated by three sensors-Inositol Requiring Enzyme 1 (IRE1), Activating Transcription Factor 6 (ATF6), and Protein Kinase RNA-Like Endoplasmic Reticulum Kinase (PERK)—allows restoring protein homeostasis and maintaining cell survival. UPR represents a major cytoprotective signaling network for cancer cells, which frequently experience disturbed proteostasis owing to their rapid proliferation in an usually unfavorable microenvironment. Increased basal UPR also participates in the resistance of tumor cells against chemotherapy. UPR activation also occurs during hematopoiesis, and growing evidence supports the critical cytoprotective role played by ER stress in the emergence and proliferation of leukemic cells. In case of severe or prolonged stress, pro-survival UPR may however evolve into a cell death program called terminal UPR. Interestingly, a large number of studies have revealed that the induction of proapoptotic UPR can also strongly contribute to the sensitization of leukemic cells to chemotherapy. Here, we review the current knowledge on the consequences of the deregulation of UPR signaling in leukemias and their implications for the treatment of these diseases.

ER Stress-Sensor Proteins and ER-Mitochondrial Crosstalk-Signaling Beyond (ER) Stress Response

Recent studies undoubtedly show the importance of inter organellar connections to maintain cellular homeostasis. In normal physiological conditions or in the presence of cellular and environmental stress, each organelle responds alone or in coordination to maintain cellular function. The Endoplasmic reticulum (ER) and mitochondria are two important organelles with very specialized structural and functional properties. These two organelles are physically connected through very specialized proteins in the region called the mitochondria-associated ER membrane (MAM). The molecular foundation of this relationship is complex and involves not only ion homeostasis through the shuttling of calcium but also many structural and apoptotic proteins. IRE1alpha and PERK are known for their canonical function as an ER stress sensor controlling unfolded protein response during ER stress. The presence of these transmembrane proteins at the MAM indicates its potential involvement in other biological functions beyond ER stress signaling. Many recent studies have now focused on the non-canonical function of these sensors. In this review, we will focus on ER mitochondrial interdependence with special emphasis on the non-canonical role of ER stress sensors beyond ER stress.

ER Disposal Pathways in Chronic Liver Disease: Protective, Pathogenic, and Potential Therapeutic Targets

The endoplasmic reticulum is a central player in liver pathophysiology. Chronic injury to the ER through increased lipid content, alcohol metabolism, or accumulation of misfolded proteins causes ER stress, dysregulated hepatocyte function, inflammation, and worsened disease pathogenesis. A key adaptation of the ER to resolve stress is the removal of excess or misfolded proteins. Degradation of intra-luminal or ER membrane proteins occurs through distinct mechanisms that include ER-associated Degradation (ERAD) and ER-to-lysosome-associated degradation (ERLAD), which includes macro-ER-phagy, micro-ER-phagy, and Atg8/LC-3-dependent vesicular delivery. All three of these processes are critical for removing misfolded or unfolded protein aggregates, and re-establishing ER homeostasis following expansion/stress, which is critical for liver function and adaptation to injury. Despite playing a key role in resolving ER stress, the contribution of these degradative processes to liver physiology and pathophysiology is understudied. Analysis of publicly available datasets from diseased livers revealed that numerous genes involved in ER-related degradative pathways are dysregulated; however, their roles and regulation in disease progression are not well defined. Here we discuss the dynamic regulation of ER-related protein disposal pathways in chronic liver disease and cell-type specific roles, as well as potentially targetable mechanisms for treatment of chronic liver disease.

X-box-binding protein 1 is required for pancreatic development in Xenopus laevis

X-box-binding protein 1 (XBP1) is a protein containing the basic leucine zipper structure. It belongs to the cAMP-response element binding protein (CREB)/activating transcription factor transcription factor family. As the main transcription factor, spliced XBP1 (XBP1s) participates in many physiological and pathological processes and plays an important role in embryonic development. Previous studies showed that XBP1-knockout mice died because of pancreatic exocrine function deficiency, indicating that XBP1 plays an important role in pancreatic development. However, the exact role of XBP1 in pancreatic development remains unclear. This study aimed to investigate the role of XBP1 in the pancreatic development of Xenopus laevis embryos. Whole-mount in situ hybridization and quantitative real-time PCR results revealed that the expression levels of pancreatic progenitor marker genes pdx1, p48, ngn3, and sox9 were downregulated in XBP1s morpholino oligonucleotide (MO)-injected embryos. The expression levels of pancreatic exocrine and endocrine marker genes insulin and amylase were also downregulated. Through the overexpression of XBP1s, the phenotype and gene expressions were opposite to those in XBP1s MO-injected embryos. Luciferase and chromatin immunoprecipitation assays showed that XBP1s could bind to the XBP1-binding site in the foxa2 promoter. These results revealed that XBP1 is required in the pancreatic development of Xenopus laevis and might function by regulating foxa2.

Inositol-requiring enzyme 1 (IRE1) plays for AvrRpt2-triggered immunity and RIN4 cleavage in Arabidopsis under endoplasmic reticulum (ER) stress

Many stresses induce the accumulation of unfolded and misfolded proteins in the endoplasmic reticulum, a phenomenon known as ER stress. In response to ER stress, cells initiate a protective response, known as unfolded protein response (UPR), to maintain cellular homeostasis. The UPR sensor, inositol-requiring enzyme 1 (IRE1), catalyzes the cytoplasmic splicing of bZIP transcription factor-encoding mRNAs to activate the UPR signaling pathway. Recently, we reported that pretreatment of Arabidopsis thaliana plants with tunicamycin, an ER stress inducer, increased their susceptibility to bacterial pathogens; on the other hand, IRE1 deficient mutants were susceptible to Pseudomonas syringae pv. maculicola (Psm) and failed to induce salicylic acid (SA)-mediated systemic acquired resistance. However, the functional relationship of IRE1 with the pathogen and TM treatment remains unknown. In the present study, we showed that bacterial pathogen-associated molecular patterns (PAMPs) induced IRE1 expression; however, PAMP-triggered immunity (PTI) response such as callose deposition, PR1 protein accumulation, or Pst DC3000 hrcC growth was not altered in ire1 mutants. We observed that IRE1 enhanced plant immunity against the bacterial pathogen P. syringae pv. tomato DC3000 (Pst DC3000) under ER stress. Moreover, TM-pretreated ire1 mutants were more susceptible to the avirulent strain Pst DC3000 (AvrRpt2) and showed greater cell death than wild-type plants during effector-triggered immunity (ETI). Additionally, Pst DC3000 (AvrRpt2)-mediated RIN4 degradation was reduced in ire1 mutants under TM-induced ER stress. Collectively, our results reveal that IRE1 plays a pivotal role in the immune signaling pathway to activate plant immunity against virulent and avirulent bacterial strains under ER stress.

High-level production of glucose oxidase in Pichia pastoris: Effects of Hac1p overexpression on cell physiology and enzyme expression

Secretion is a common bottleneck in the production of industrial proteins. Although overexpression of the unfolded protein response regulator Hac1p has been widely used to enhance protein secretion, its effects on the physiology of host cells were often overlooked, which would attenuate and even neutralize its beneficial effects on overall protein production. In order to achieve high-level glucose oxidase (GOX) production in Pichia pastoris, we used a set of Hac1p homologues from Saccharomyces cerevisiae (ScHac1p), P. pastoris (PpHac1p), Trichoderma reesei (TrHac1p) and Homo sapiens (HsXbp1), to evaluate the effects of Hac1p overexpression on the secretion capacity, cell physiology and overall enzyme production in P. pastoris strains containing different copies of the GOX gene. Results showed that overexpression of Hac1ps was able to remarkably alleviate the secretion bottleneck in the 3-copy strain, to improve its GOX secretion capacity by 21.2-140.2 % and its overall enzyme production by 23.7-69.2 %. However, overexpression of ScHac1p, PpHac1p and TrHac1p led to reduced cell growth in GS-3GOX, possibly due to increased oxidative stress. Overexpression of ScHac1p and PpHac1p in the 6-copy strain (resulting in GS-6GOX-Sc and GS-6GOX-Pp, respectively) further increased the overall GOX production levels by 88.9-103.3 %, and GS-6GOX-Pp exhibited the highest overall GOX production and GOX secretion capacity among all constructed strains. Nevertheless, in addition of significantly reduced growth, loss of GOX gene was also observed for GS-6GOX-Pp and GS-6GOX-Sc during the fermentation process. With higher induction cell density and co-feeding of yeast extract, the GOX titer of GS-6GOX-Pp reached 2125.3 U/mL on 1-liter fermentor. This study not only achieves a record high GOX production level but also provides new insights into secretion pathway engineering using Hac1p overexpression strategy.

The unfolded protein response modulates the autophagy-mediated egg production in the mosquito Aedes aegypti

Mosquitoes must feed on vertebrate blood for egg development. As a consequence, some mosquito species are vectors for pathogens that cause devastating diseases in humans. Hence, understanding the mechanisms that control egg developmental cycles is important for developing novel approaches for the control of mosquito-borne diseases. The unfolded protein response (UPR) is a cellular stress response related to endoplasmic reticulum (ER) stress. The UPR is activated in response to an accumulation of unfolded or misfolded proteins in the ER. Massive proteins have been shown to be produced during egg development, and it is obvious that unfolded or misfolded proteins may arise during vitellogenesis. It has been shown that autophagy in the mosquito fat body plays a central role in the progression of gonadotrophic cycles in the mosquito Aedes aegypti. However, the molecular mechanisms underlying the induction of UPR and the correlation between UPR and autophagy remain unclear. Here, we demonstrate that autophagy is activated during vitellogenesis and that the activation of autophagy is correlated with the UPR. We also show that the expressions of UPR and autophagy can be induced in an in vitro fat body culture system through an amino acid treatment. In addition, the expressions of UPR, autophagy-specific markers and vitellogenin were also induced during dithiothreitol treatment. Interestingly, the silencing of UPR-related genes significantly reduced the expression of autophagy-specific markers and inhibited mosquito fecundity. Taken together, we conclude that autophagy-mediated egg production in the mosquito A. aegypti is regulated by UPR.

The UPR in Neurodegenerative Disease: Not Just an Inside Job

Neurons are highly specialized cells that continuously and extensively communicate with other neurons, as well as glia cells. During their long lifetime, the post-mitotic neurons encounter many stressful situations that can disrupt protein homeostasis (proteostasis). The importance of tight protein quality control is illustrated by neurodegenerative disorders where disturbed neuronal proteostasis causes neuronal dysfunction and loss. For their unique function, neurons require regulated and long-distance transport of membrane-bound cargo and organelles. This highlights the importance of protein quality control in the neuronal endomembrane system, to which the unfolded protein response (UPR) is instrumental. The UPR is a highly conserved stress response that is present in all eukaryotes. However, recent studies demonstrate the existence of cell-type-specific aspects of the UPR, as well as cell non-autonomous UPR signaling. Here we discuss these novel insights in view of the complex cellular architecture of the brain and the implications for neurodegenerative diseases.

Functional Coupling between the Unfolded Protein Response and Endoplasmic Reticulum/Golgi Ca2+-ATPases Promotes Stress Tolerance, Cell Wall Biosynthesis, and Virulence of Aspergillus fumigatus

Many species of pathogenic fungi deploy the unfolded protein response (UPR) to expand the folding capacity of the endoplasmic reticulum (ER) in proportion to the demand for virulence-related proteins that traffic through the secretory pathway. Although Ca²⁺ plays a pivotal role in ER function, the mechanism by which transcriptional upregulation of the protein folding machinery is coordinated with Ca²⁺ homeostasis is incompletely understood. In this study, we investigated the link between the UPR and genes encoding P-type Ca²⁺-ATPases in the human-pathogenic mold Aspergillus fumigatus We demonstrate that acute ER stress increases transcription of the srcA gene, encoding a member of the sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) family, as well as that of pmrA, encoding a secretory pathway Ca²⁺-ATPase (SPCA) in the Golgi membrane. Loss of the UPR transcription factor HacA prevented the induction of srcA and pmrA transcription during ER stress, defining these ER/Golgi Ca²⁺ pumps as novel downstream targets of this pathway. While deletion of srcA alone caused no major deficiencies, a ΔsrcA/ΔpmrA mutant displayed a severe polarity defect, was hypersensitive to ER stress, and showed attenuated virulence. In addition, cell wall analyses revealed a striking reduction in mannose levels in the absence of both Ca²⁺ pumps. The ΔhacA mutant was hypersensitive to agents that block calcineurin-dependent signaling, consistent with a functional coupling between the UPR and Ca²⁺ homeostasis. Together, these findings demonstrate that the UPR integrates the need for increased levels of chaperone and folding enzymes with an influx of Ca²⁺ into the secretory pathway to support fungal growth, stress adaptation, and pathogenicity.IMPORTANCE The UPR is an intracellular signal transduction pathway that maintains homeostasis of the ER. The pathway is also tightly linked to the expression of virulence-related traits in diverse species of human-pathogenic and plant-pathogenic fungal species, including the predominant mold pathogen infecting humans, Aspergillus fumigatus Despite advances in the understanding of UPR signaling, the linkages and networks that are governed by this pathway are not well defined. In this study, we revealed that the UPR is a major driving force for stimulating Ca²⁺ influx at the ER and Golgi membranes and that the coupling between the UPR and Ca²⁺ import is important for virulence, cell wall biosynthesis, and resistance to antifungal compounds that inhibit Ca²⁺ signaling.

Ribosome-associated vesicles: A dynamic subcompartment of the endoplasmic reticulum in secretory cells

The endoplasmic reticulum (ER) is a highly dynamic network of membranes. Here, we combine live-cell microscopy with in situ cryo-electron tomography to directly visualize ER dynamics in several secretory cell types including pancreatic β-cells and neurons under near-native conditions. Using these imaging approaches, we identify a novel, mobile form of ER, ribosome-associated vesicles (RAVs), found primarily in the cell periphery, which is conserved across different cell types and species. We show that RAVs exist as distinct, highly dynamic structures separate from the intact ER reticular architecture that interact with mitochondria via direct intermembrane contacts. These findings describe a new ER subcompartment within cells.

HacA Governs Virulence Traits and Adaptive Stress Responses in Trichophyton rubrum

The ability of fungi to sense environmental stressors and appropriately respond is linked to secretory system functions. The dermatophyte infection process depends on an orchestrated signaling regulation that triggers the transcription of genes responsible for adherence and penetration of the pathogen into host-tissue. A high secretion system is activated to support the host-pathogen interaction and assures maintenance of the dermatophyte infection. The gateway of secretion machinery is the endoplasmic reticulum (ER), which is the primary site for protein folding and transport. Current studies have shown that ER stress that affects adaptive responses is primarily regulated by UPR and supports fungal pathogenicity; this has been assessed for yeasts and Aspergillus fumigatus, in regard to how these fungi cope with host environmental stressors. Fungal UPR consists of a transmembrane kinase sensor (Ire1/IreA) and a downstream target Hac1/HacA. The active form of Hac is achieved via non-spliceosomal intron removal promoted by endonuclease activity of Ire1/IreA. Here, we assessed features of HacA and its involvement in virulence and susceptibility in Trichophyton rubrum. Our results showed that exposure to antifungals and ER-stressing agents initiated the activation of HacA from T. rubrum. Interestingly, the activation occurs when a 20 nt fragment is removed from part of the exon-2 and part of intron-2, which in turn promotes the arisen of the DNA binding site motif and a dimer interface domain. Further, we found changes in the cell wall and cellular membrane composition in the ΔhacA mutant as well as an increase in susceptibility toward azole and cell wall disturbing agents. Moreover, the ΔhacA mutant presented significant defects in important virulence traits like thermotolerance and growth on keratin substrates. For instance, the development of the ΔhacA mutant was impaired in co-culture with keratinocytes or human nail fragments. Changes in the pro-inflammatory cytokine release were verified for the ΔhacA mutant during the co-culture assay, which might be related to differences in pathogen-associated molecular patterns (PAMPs) in the cell wall. Together, these results suggested that HacA is an integral part of T. rubrum physiology and virulence, implying that it is an important molecular target for antidermatophytic therapy.

The ER Unfolded Protein Response Effector, ATF6, Reduces Cardiac Fibrosis and Decreases Activation of Cardiac Fibroblasts

Activating transcription factor-6 α (ATF6) is one of the three main sensors and effectors of the endoplasmic reticulum (ER) stress response and, as such, it is critical for protecting the heart and other tissues from a variety of environmental insults and disease states. In the heart, ATF6 has been shown to protect cardiac myocytes. However, its roles in other cell types in the heart are unknown. Here we show that ATF6 decreases the activation of cardiac fibroblasts in response to the cytokine, transforming growth factor β (TGFβ), which can induce fibroblast trans-differentiation into a myofibroblast phenotype through signaling via the TGFβ–Smad pathway. ATF6 activation suppressed fibroblast contraction and the induction of α smooth muscle actin (αSMA). Conversely, fibroblasts were hyperactivated when ATF6 was silenced or deleted. ATF6 thus represents a novel inhibitor of the TGFβ–Smad axis of cardiac fibroblast activation.

Altered Expression of Adrenomedullin 2 and its Receptor in the Adipose Tissue of Obese Patients

CONTEXT

Adrenomedullin 2 (AM2) plays protective roles in the renal and cardiovascular systems. Recent studies in experimental animals demonstrated that AM2 is an adipokine with beneficial effects on energy metabolism. However, there is little information regarding AM2 expression in human adipose tissue.

OBJECTIVE

To investigate the pattern and regulation of the expression of AM2 and its receptor component in human adipose tissue, in the context of obesity and type 2 diabetes.

METHODS

We measured metabolic parameters, serum AM2, and expression of ADM2 and its receptor component genes in abdominal subcutaneous and visceral adipose tissue in obese (with or without type 2 diabetes) and normal-weight women. Serum AM2 was assessed before and 6 to 9 months after bariatric surgery. Expression/secretion of AM2 and its receptor were assessed in human adipocytes.

RESULTS

ADM2 mRNA in both fat depots was higher in obese patients, whether diabetic or not. Although serum AM2 was significantly lower in obese patients, it was not changed after bariatric surgery. AM2 and its receptor complex were predominantly expressed by adipocytes, and the expression of CALCRL, encoding a component of the AM2 receptor complex, was lower in both fat depots of obese patients. Incubating adipocytes with substances mimicking the microenvironment of obese adipose tissue increased ADM2 mRNA but reduced both AM2 secretion into culture media and CALCRL mRNA expression.

CONCLUSIONS

Our data indicate that AM2 signaling is suppressed in adipose tissue in obesity, involving lower receptor expression and ligand availability, likely contributing to insulin resistance and other aspects of the pathophysiology associated with obesity.

Nutrient Sensor mTOR and OGT: Orchestrators of Organelle Homeostasis in Pancreatic β-Cells

The purpose of this review is to integrate the role of nutrient-sensing pathways into β-cell organelle dysfunction prompted by nutrient excess during type 2 diabetes (T2D). T2D encompasses chronic hyperglycemia, hyperlipidemia, and inflammation, which each contribute to β-cell failure. These factors can disrupt the function of critical β-cell organelles, namely, the ER, mitochondria, lysosomes, and autophagosomes. Dysfunctional organelles cause defects in insulin synthesis and secretion and activate apoptotic pathways if homeostasis is not restored. In this review, we will focus on mTORC1 and OGT, two major anabolic nutrient sensors with important roles in β-cell physiology. Though acute stimulation of these sensors frequently improves β-cell function and promotes adaptation to cell stress, chronic and sustained activity disturbs organelle homeostasis. mTORC1 and OGT regulate organelle function by influencing the expression and activities of key proteins, enzymes, and transcription factors, as well as by modulating autophagy to influence clearance of defective organelles. In addition, mTORC1 and OGT activity influence islet inflammation during T2D, which can further disrupt organelle and β-cell function. Therapies for T2D that fine-tune the activity of these nutrient sensors have yet to be developed, but the important role of mTORC1 and OGT in organelle homeostasis makes them promising targets to improve β-cell function and survival.

Impact of Bevacizumab on Liver Damage After Massive Hepatectomy in Rats

BACKGROUND

The aim of this study was to evaluate the impact of pretreatment with bevacizumab on liver damage in a rat model of massive hepatectomy (Hx) model, as a surrogate model of massive Hx for liver metastasis from colorectal cancer.

MATERIALS AND METHODS

Male Wister rats (n=24) were separated into the following two groups: 90% Hx and 90% Hx plus bevacizumab group. Bevacizumab (5 mg/kg) was injected intraperitoneally 7 days before Hx. Samples of blood and remnant liver tissue were obtained 24 hours after hepatectomy and the following parameters were evaluated: Biochemical analysis; liver regeneration rate; survival rate; and real-time polymerase chain reaction for interleukin-1 beta (Il1b), tumor necrosis factor alpha (Tnfa), matrix metalloproteinase (Mmp) 2 and Mmp9 mRNA. In addition, samples of whole liver tissue were obtained immediately before Hx and real-time polymerase chain reaction was performed for X-box binding protein 1 (Xbp1), activating transcription factor 6 (Atf6), C/EBP homologous protein (Chop), glucose-regulated protein 78 (Grp78) and heat-shock protein 70 (Hsp70), as markers of endoplasmic reticulum stress response.

RESULTS

The levels of transaminases 24 hours after Hx were significantly reduced in the group pretreated with bevacizumab compared to that not pretreated (p<0.05). The liver regeneration rate at 24 hours after Hx was significantly increased in the group pretreated with bevacizumab compared with the group which underwent Hx alone (p<0.05). The survival rate for the group pretreated with bevacizumab tended to be higher than that of the Hx-only group, 72 hours after Hx (p=0.09). The expressions of Il1b, Mmp2 and Mmp9 mRNA 24 hours after Hx in the group pretreated with bevacizumab tended to be lower than that of rats which underwent Hx alone (p=0.11, 0.09 and 0.15, respectively). The expression of Xbp1, Chop, Grp78 and Hsp70 mRNA immediately before Hx in the group pretreated with bevacizumab were significantly higher than the 90% Hx group (p<0.05).

CONCLUSION

Bevacizumab pretreatment had protective effects on liver injury after massive hepatectomy in rats, apparently via the induction of the endoplasmic reticulum stress response, i.e. the so-called unfolded protein response.

24(S)-Hydroxycholesterol induces ER dysfunction-mediated unconventional cell death

Endoplasmic reticulum (ER) stress induced by disruption of protein folding activates the unfolded protein response (UPR), which while generally pro-survival in effect can also induce cell death under severe ER stress. 24(S)-hydroxycholesterol (24S-OHC), which is enzymatically produced in the ER of neurons, plays an important role in maintaining brain cholesterol homeostasis but also shows neurotoxicity when subjected to esterification by acyl-CoA:cholesterol acyltransferase 1 (ACAT1) in the ER. In this study, we demonstrated that the accumulation of 24S-OHC esters in human neuroblastoma SH-SY5Y cells evoked the UPR with substantially no pro-survival adaptive response but with significant activation of pro-death UPR signaling via regulated IRE1-dependent decay (RIDD). We further found that accumulation of 24S-OHC esters caused disruption of ER membrane integrity and release of ER luminal proteins into cytosol. We also found that de novo synthesis of global proteins was robustly suppressed in 24S-OHC-treated cells. Collectively, these results show that ER dysfunction and the accompanying RIDD-mediated pro-death UPR signaling and global protein synthesis inhibition are responsible for 24S-OHC ester-induced unconventional cell death.

Human placenta-derived mesenchymal stem cells inhibit apoptosis of granulosa cells induced by IRE1α pathway in autoimmune POF mice

Previous studies have shown that the ovarian failure in autoimmune-induced premature ovarian failure (POF) mice could be improved by the transplantation of human placenta-derived mesenchymal stem cells (hPMSCs); however, the protective mechanism of hPMSCs transplantation on ovarian dysfunction remains unclear. Ovarian dysfunction is closely related to the apoptosis of granulosa cells (GCs). To determine the effects of hPMSCs transplantation on GCs apoptosis, an autoimmune POF mice model was established with zona pellucida glycoprotein 3 (ZP3) peptide. It is reported that the inositol-requiring enzyme 1α (IRE1α) and its downstream molecules play a central role in the endoplasmic reticulum (ER) stress-induced apoptosis pathway. So the aim of this study is to investigate whether hPMSCs transplantation attenuated GCs apoptosis via inhibiting ER stress IRE1α signaling pathway. The ovarian dysfunction, follicular dysplasia, and GCs apoptosis were observed in the POF mice. And the IRE1α pathway was activated in ovaries of POF mice, as demonstrated by, increased X-box binding protein 1 (XBP1), up-regulated 78 kDa glucose-regulated protein (GRP78) and caspase-12. Following transplantation of hPMSCs, the ovarian structure and function were significantly improved in POF mice. In addition, the GCs apoptosis was obviously attenuated and IRE1α pathway was significantly inhibited. Transplantation of hPMSCs suppressed GCs apoptosis-induced by ER stress IRE1α signaling pathway in POF mice, which might contribute to the hPMSCs transplantation-mediating ovarian function recovery.

The Best for the Most Important: Maintaining a Pristine Proteome in Stem and Progenitor Cells

Pluripotent stem cells give rise to reproductively enabled offsprings by generating progressively lineage-restricted multipotent stem cells that would differentiate into lineage-committed stem and progenitor cells. These lineage-committed stem and progenitor cells give rise to all adult tissues and organs. Adult stem and progenitor cells are generated as part of the developmental program and play critical roles in tissue and organ maintenance and/or regeneration. The ability of pluripotent stem cells to self-renew, maintain pluripotency, and differentiate into a multicellular organism is highly dependent on sensing and integrating extracellular and extraorganismal cues. Proteins perform and integrate almost all cellular functions including signal transduction, regulation of gene expression, metabolism, and cell division and death. Therefore, maintenance of an appropriate mix of correctly folded proteins, a pristine proteome, is essential for proper stem cell function. The stem cells' proteome must be pristine because unfolded, misfolded, or otherwise damaged proteins would interfere with unlimited self-renewal, maintenance of pluripotency, differentiation into downstream lineages, and consequently with the development of properly functioning tissue and organs. Understanding how various stem cells generate and maintain a pristine proteome is therefore essential for exploiting their potential in regenerative medicine and possibly for the discovery of novel approaches for maintaining, propagating, and differentiating pluripotent, multipotent, and adult stem cells as well as induced pluripotent stem cells. In this review, we will summarize cellular networks used by various stem cells for generation and maintenance of a pristine proteome. We will also explore the coordination of these networks with one another and their integration with the gene regulatory and signaling networks.

Anti-tumor Efficacy Assessment of the Sigma Receptor Pan Modulator RC-106. A Promising Therapeutic Tool for Pancreatic Cancer

Introduction: Pancreatic cancer (PC) is one of the most lethal tumor worldwide, with no prognosis improvement over the past 20-years. The silent progressive nature of this neoplasia hampers the early diagnosis, and the surgical resection of the tumor, thus chemotherapy remains the only available therapeutic option. Sigma receptors (SRs) are a class of receptors proposed as new cancer therapeutic targets due to their over-expression in tumor cells and their involvement in cancer biology. The main localization of these receptors strongly suggests their potential role in ER unfolded protein response (ER-UPR), a condition frequently occurring in several pathological settings, including cancer. Our group has recently identified RC-106, a novel pan-SR modulator with good in vitro antiproliferative activities toward a panel of different cancer cell lines. In the present study, we investigated the in vitro properties and pharmacological profile of RC-106 in PC cell lines with the aim to identify a potential lead candidate for the treatment of this tumor.

Methods: Pancreatic cancer cell lines Panc-1, Capan-1, and Capan-2 have been used in all experiments. S1R and TMEM97/S2R expression in PC cell lines was quantified by Real-Time qRT-PCR and Western Blot experiments. MTS assay was used to assess the antiproliferative effect of RC-106. The apoptotic properties of RC-106 was evaluated by TUNEL and caspase activation assays. GRP78/BiP, ATF4, and CHOP was quantified to evaluate ER-UPR. Proteasome activity was investigated by a specific fluorescent-based assay. Scratch wound healing assay was used to asses RC-106 effect on cell migration. In addition, we delineated the in vivo pharmacokinetic profile and pancreas distribution of RC-106 in male CD-1 mice.

Results: Panc-1, Capan-1, and Capan-2 express both SRs. RC-106 exerts an antiproliferative and pro-apoptotic effect in all examined cell lines. Cells exposure to RC-106 induces the increase of the expression of ER-UPR related proteins, and the inhibition of proteasome activity. Moreover, RC-106 is able to decrease PC cell lines motility. The in vivo results show that RC-106 is more concentrated in pancreas than plasma.

Conclusion: Overall, our data evidenced that the pan-SR modulator RC-106 is an optimal candidate for in vivo studies in animal models of PC.

Lipid bilayer stress and proteotoxic stress-induced unfolded protein response deploy divergent transcriptional and non-transcriptional programmes

The unfolded protein response (UPR) is activated by endoplasmic reticulum (ER) stress and is designed to restore cellular homeostasis through multiple intracellular signalling pathways. In mammals, the UPR programme regulates the expression of hundreds of genes in response to signalling from ATF6, IRE1, and PERK. These three highly conserved stress sensors are activated by the accumulation of unfolded proteins within the ER. Alternatively, IRE1 and PERK sense generalised lipid bilayer stress (LBS) at the ER while ATF6 is activated by an increase of specific sphingolipids. As a result, the UPR supports cellular robustness as a broad-spectrum compensatory pathway that is achieved by deploying a tailored transcriptional programme adapted to the source of ER stress. This review summarises the current understanding of the three ER stress transducers in sensing proteotoxic stress and LBS. The plasticity of the UPR programme in the context of different sources of ER stress will also be discussed.

The PERK-EIF2α-ATF4 signaling branch regulates osteoblast differentiation and proliferation by PTH

Parathyroid hormone (PTH) and its related peptide (PTH-related peptide 1-34) are two of the Food and Drug Administration-approved bone-promoting drugs for age-related osteoporosis. Treatment with PTH stimulates bone formation. However, the molecular mechanisms of PTH-mediated osteoblast differentiation and cell proliferation are still not completely understood. In this study, we showed that PTH induced endoplasmic reticulum (ER) stress in osteoblasts through the PKR-like endoplasmic reticulum kinase (PERK)-eukaryotic initiation factor 2α (EIF2α)-activating transcription factor 4 (ATF4)-signaling pathway. After separately blocking PERK-EIF2α-ATF4 signaling with two different inhibitors [AMG'44 and integrated stress response inhibitor (ISRIB)] or specific small interfering RNA for PERK and ATF4, the following targets were all downregulated: expression of osteoblast differentiation markers [runt-related transcription factor 2 (Runx2), alkaline phosphatase (Alp), type I collagen (Col1a1), and osteocalcin (Ocn)], cell proliferation markers (CyclinE, CyclinD, and CDC2), amino acid import (Glyt1), and metabolism-related genes (Asns). Additionally, Alp-positive staining cells, Alp activity, matrix mineralization, Ocn secretion, and cell proliferation indexes were inhibited. Interestingly, we found that salubrinal enhanced PTH-induced osteoblast differentiation and proliferation by maintenance of phosphorylation of EIF2α. Furthermore, we observed that PTH increased the association between heat shock protein 90 (HSP90) and PERK and maintained PERK protein stabilization in the early stages of PTH-induced ER stress. Treatment of MC3T3-E1 cells with geldanamycin, an HSP90 inhibitor, decreased PERK protein expression and inhibited osteoblast differentiation and cell proliferation upon PTH treatment. Taken together, our data demonstrate that PTH regulates osteoblast differentiation and cell proliferation, partly by activating the HSP90-dependent PERK-EIF2α-ATF4 signaling pathway.